Welding is used to join two or more pieces of material together, to repair defects in the surface of a single piece of material, and to build up structures. In the first two applications, the welding may be accomplished by heating the piece(s) to either join them or to heal the defect, without adding additional material. The welding in each case may instead be accomplished by melting additional material, termed a filler metal, that subsequently is solidified to join the pieces or to fill the defect in the single piece or to build up a structure. The filler metal is usually supplied as a powder that is injected into the heated region being welded, or as a welding rod that is gradually fed into the heated region. The filler metal may be of the same composition as the piece or pieces being welded, or of a different composition.
There is sometimes a distinction made between “welding rod”, taken to be of larger diameter, and “welding wire”, taken to be of smaller diameter. As used herein to avoid any arbitrary distinction between them, the terms “rod” and “welding rod” include both larger-diameter and smaller-diameter forms of rod and welding-feed materials, and thence includes both what is sometimes referred to as welding rod and what is sometimes referred to as welding wire.
Most welding rod is made by melting the metallic alloy that is to form the welding rod, casting the molten alloy into a cast form, and then wire drawing the cast form to its final diameter and length. However, this approach is limited to those metallic alloys that are sufficiently ductile to be wire drawn without failing. For less-ductile alloys, such as some high-gamma-prime superalloys that are to be used as welding rod, the cast or powder-processed metallic alloy is extruded to its final form.